The weight of the cold is also very small, but heavier then the normal air.

Then they turned off the gas and let them breathe normal air again.

He stifled the urge to rise up for a breath of normal air.

First his lungs had lost their adaptation to normal air.

The child finally came to Snow, who explained that he would have to survive on normal air.

Note that 21% is the concentration of oxygen in normal air.

I opened my eyes, as if to breathe through them, so breathless did normal air leave me then.

The purpose of this gas is to keep normal air out, especially oxygen.

Why don't they use normal air in race car tires?

I think concentrators do not provide 100% oxygen, rather more like 40%, up from the usual 20% that is in normal air.